Manufacturing method of semiconductor device

Abstract

A manufacturing method of a semiconductor device includes the following steps. A first recess and a second recess are formed in a first region and a second region of a semiconductor substrate, respectively. A bottom surface of the first recess is lower than a bottom surface of the second recess in a vertical direction. A first gate oxide layer and a second gate oxide layer are formed concurrently. At least a portion of the first gate oxide layer is formed in the first recess, and at least a portion of the second gate oxide layer is formed in the second recess. A removing process is performed for removing a part of the second gate oxide layer. A thickness of the second gate oxide layer is less than a thickness of the first gate oxide layer after the removing process.

What is claimed is: 
     
       1. A manufacturing method of a semiconductor device, comprising:
 forming a first recess in a first region of a semiconductor substrate; 
 forming a second recess in a second region of the semiconductor substrate, wherein a bottom surface of the first recess is lower than a bottom surface of the second recess in a vertical direction, and the first recess and the second recess are formed concurrently; 
 forming a first gate oxide layer and a second gate oxide layer concurrently, wherein at least a portion of the first gate oxide layer is formed in the first recess, and at least a portion of the second gate oxide layer is formed in the second recess; 
 performing a removing process for removing a part of the second gate oxide layer, wherein a thickness of the second gate oxide layer is less than a thickness of the first gate oxide layer after the removing process; 
 forming a pad oxide layer on the semiconductor substrate before the first recess and the second recess are formed, wherein a first portion of the pad oxide layer is formed on the first region of the semiconductor substrate, a second portion of the pad oxide layer is formed on the second region of the semiconductor substrate, and a third portion of the pad oxide layer is formed on a third region of the semiconductor substrate; and 
 removing the third portion of the pad oxide layer after the first gate oxide layer and the second gate oxide layer are formed and before the removing process. 
 
     
     
       2. The manufacturing method of the semiconductor device according to  claim 1 , wherein a bottom surface of the first gate oxide layer is lower than a bottom surface of the second gate oxide layer in the vertical direction. 
     
     
       3. The manufacturing method of the semiconductor device according to  claim 1 , wherein a top surface of the second gate oxide layer is higher than a top surface of the first gate oxide layer in the vertical direction before the removing process. 
     
     
       4. The manufacturing method of the semiconductor device according to  claim 1 , wherein the first portion and the second portion of the pad oxide layer are removed by the removing process. 
     
     
       5. The manufacturing method of the semiconductor device according to  claim 1 , further comprising:
 forming a third gate oxide layer on the third region of the semiconductor substrate after the third portion of the pad oxide layer is removed and before the removing process. 
 
     
     
       6. The manufacturing method of the semiconductor device according to  claim 5 , wherein a thickness of the third gate oxide layer is less than the thickness of the second gate oxide layer before and after the removing process. 
     
     
       7. The manufacturing method of the semiconductor device according to  claim 5 , wherein a bottom surface of the third gate oxide layer is higher than a bottom surface of the first gate oxide layer and a bottom surface of the second gate oxide layer in the vertical direction. 
     
     
       8. The manufacturing method of the semiconductor device according to  claim 5 , further comprising:
 forming a patterned mask layer on the semiconductor substrate before the removing process, wherein the first gate oxide layer and the third gate oxide layer are covered by the patterned mask layer during the removing process. 
 
     
     
       9. The manufacturing method of the semiconductor device according to  claim 1 , further comprising:
 forming a third recess in first region of the semiconductor substrate; and 
 forming a fourth recess in the third region of the semiconductor substrate, wherein the third recess and the fourth recess are formed concurrently before the pad oxide layer is formed, the third portion of the pad oxide layer is formed in the fourth recess, and the first portion of the pad oxide layer is partly formed in the third recess and partly formed outside the third recess. 
 
     
     
       10. The manufacturing method of the semiconductor device according to  claim 9 , wherein the first portion of the pad oxide layer located in the third recess is lower than the second portion of the pad oxide layer in the vertical direction. 
     
     
       11. The manufacturing method of the semiconductor device according to  claim 9 , wherein the first portion of the pad oxide layer located in the third recess is removed by a process of forming the first recess, and the second portion of the pad oxide layer is removed by a process of forming the second recess. 
     
     
       12. The manufacturing method of the semiconductor device according to  claim 1 , further comprising:
 forming a first isolation structure in the first region of the semiconductor substrate; and 
 forming a second isolation structure in the second region of the semiconductor substrate, wherein the first isolation structure comprises a protruding part extending downwards, and the protruding part is lower than a bottom surface of the second isolation structure in the vertical direction. 
 
     
     
       13. The manufacturing method of the semiconductor device according to  claim 12 , wherein the first isolation structure is directly connected with the first gate oxide layer, and the second isolation structure is directly connected with the second gate oxide layer. 
     
     
       14. The manufacturing method of the semiconductor device according to  claim 12 , wherein a part of the first isolation structure and a part of the second isolation structure are removed by the removing process. 
     
     
       15. The manufacturing method of the semiconductor device according to  claim 12 , further comprising:
 forming a patterned mask layer on the semiconductor substrate before the removing process, wherein the first gate oxide layer, a part of the first isolation structure, and a part of the second isolation structure are covered by the patterned mask layer during the removing process. 
 
     
     
       16. The manufacturing method of the semiconductor device according to  claim 1 , wherein a portion of the second gate oxide layer is formed outside the second recess and removed by the removing process. 
     
     
       17. The manufacturing method of the semiconductor device according to  claim 1 , wherein the removing process comprises a dry etching step and a wet etching step performed after the dry etching step.